Torsional vibration dampers are commonly associated with drive mechanisms and power transfer systems, such as crankshafts of piston engines, electric motors, transmissions, drive shafts, and the like. The primary purpose of a vibration damper is to reduce the amplitude of vibrations in such systems, as excessive vibration may cause system noise, wear, fatigue and catastrophic failure. Such systems typically experience vibration from multiple sources, such as, for example, firing of different engine cylinders, crankshaft imbalances, meshing of gears in transmissions, shaft misalignment, and movement of universal joints.
Common vibration dampers include a hub for mounting the damper to a crankshaft and an annular inertia ring driven by the hub through an elastomeric member compressed between the hub and inertia ring. The outer hub rim and corresponding inner rim of the inertia ring are often coextensive and configured to provide surface area for distribution of the shear forces in the elastomer. Such dampers typically are tuned to a particular range of vibration frequencies which are determined as a function of the material properties and geometry of the elastomeric member, inertia ring and hub. Rotation of the mass of the inertia ring generates active inertia, which in combination with the cyclical stressing of the elastomer serves to resist the axial and torsional vibrational movement of the crankshaft.
One common type of damper is produced by adhering or forming the elastomeric member on either the hub or ring and by then deforming or heating the hub or inertia ring to fit within or over the corresponding hub-elastomer or inertia ring-elastomer subassembly. For example, a hub-elastomer subassembly having the elastomer molded to the peripheral face of the hub is pressed through a converging tube to radially compress the elastomeric member. The inertia ring is radially expanded through heating and is positioned around the end of the converging tube to receive the compressed hub-elastomer subassembly. The combined expansion of the elastomeric member and subsequent thermal restriction of the inertia ring create sufficient compression in the elastomeric member to secure the inertia ring to the hub. Similarly, the inertia mass may simply be press-fitted onto the hub-elastomer sub-assembly, compromising the elastomeric member.
Such assembly methods may cause defects or residual stresses or may otherwise compromise the integrity of the elastomeric member, causing premature failure of the damper. Such assembly methods also may produce imbalances in the damper, necessitating use of weights or balance drilling to properly balance the damper.
Certain inefficiencies of the damper itself may reduce the overall efficiency or lifecycle of the drive system or peripheral systems. On such inefficiency, parasitic vibration, may be caused by misalignment of a damper hub on a drive shaft or by damage or wear to the shaft or damper, such as deterioration of the elastomeric member. Similarly, parasitic vibration may be caused by irregularities, imbalances, or defects caused in the production of the damper or by subsequent deterioration caused by such defects.
Another inefficiency of conventional dampers is parasitic inertia. Parasitic inertia is generated by mass that creates a torsional load on the dampened system but does not significantly contribute to the active inertia of the damper. For example, parasitic inertia may be generated by any mass of the damper that is located radially inward of the inertia mass.
Accordingly, there exists a need for a more efficient vibration damper providing reduced parasitic vibration and reduced parasitic inertia. Similarly, a need exists for a method of manufacturing a vibration damper that does not create undue residual stresses or defects in the elastomeric member.